Williams is two wins away from her fifth U.S. Open singles title and 17th Grand Slam championship overall. She is also two wins away from her fifth U.S. Open doubles title and 16th Grand Slam doubles championship.

After winning in doubles Thursday with sister Venus 6-3, 6-1 in a quarterfinal over No. 1 seeds Sara Errani/Roberta Vinci, it stands to be a furiously busy Flushing weekend for Serena.

Friday she goes back to back. She will face the fleet Li Na of China in a 3:45 p.m semifinal. After what the USTA put on its schedule as “suitable rest,’’ Serena will return to Ashe for the doubles semifinals with her and Venus facing Andrea Hlavackova and Lucie Hradecka.

“I’m feeling great,’’ Williams said. “The doubles has really helped me. I’m excited for [Friday]. It doesn’t matter the result. I’m just excited to be healthy and playing good tennis.’’

The health remark is reference to all Williams has come back from — the remarkable rebound from blood clots in her lungs in March 2011 that nearly killed her.

That she is now aging well after a pulmonary embolism that still occasionally has to be treated for precautionary reasons is further testament to her greatness and the foundation built by her father Richard Williams.

Williams spoke a lot about her new French coach, Patrick Mouratoglou after her 6-0, 6-0 quarterfinal bageling of Carla Suarez Navarro. But she saved the kindest words for her father, who is missing his second straight Open and rarely travels any longer. Richard Williams was last seen at the WTA event in Miami near his home. He still is listed as one of her coaches, but he recently had a baby boy, Dylan, with his new second wife, Lakeisha.

“Everyone in the past who may have said my dad wasn’t a good coach, obviously the results spoke for themselves between myself and Venus,’’ Serena said. “Multiple Grand Slam titles that we have won is just — I wouldn’t have one single title without him and without his backing.’’

Some tennis experts have credited her new coach/boyfriend as a major upgrade over her father.

But not Serena. She said she still is getting advice from him via emails and phone calls.

“I think that theory went out the door years and years ago, over a decade ago,’’ Williams said. “He’s just great. He’s a great coach. Even to this day, he wrote me something just the other day and I just really meditated on it and I thought about it and I thought. This is what I need to do and it really helped me during the match.

“He’s just so innovative and I think one of the reasons I’m still playing some of the best tennis at 30 is because he built my game and my sister’s game. He gave us a good foundation. So to say he built our foundation it was solid and it wasn’t weak. So we were always able to grow our game.’’

Williams has a record of 8-1 against Li, the first Chinese player to make the Open semifinals. No. 2 seed Victoria Azarenka, the major threat to Williams’ title chances, should have an easy time against 82nd-ranked Flavia Pennetta in the other semifinal Friday.

Li has the kind of speed, court coverage and firepower that can give Williams a big test today. Li also leads the tour in aces.

“She’s a great challenge,’’ Williams said. ”She moves really well. I think the challenge of playing someone like her is how do you beat a player that does everything well. She’s been playing me really close. Maybe the next time we play she might want to go from close to a win so I have to be ready for that.’’

After accepting the U.S. Open’s sportsmanship award Friday, Li talked about her matchup with Williams.

“It’s exciting to be in semis.” Li said. “You never know what happens. People say [I] don’t have a chance but it’s a very good challenge.’’